1. Technical Field
The present invention relates to a fluid ejection device which allows switching operation between a pulsed flow ejection and a continuous flow ejection, and a method of controlling the fluid ejection device.
2. Related Art
In the related art, there are surgical instruments configured to supply liquid from a pump into a tube introduced into a body cavity at a high pressure, eject the liquid from a nozzle at a distal end of the tube, and excise tissue in the body cavity by a fluid pressure (for example, see JP-A-63-99853).
There is also proposed fluid ejection devices configured to vary the volume of a fluid chamber abruptly by a volume varying unit, transform fluid into a pulsed flow to cause the same to be ejected from a nozzle at a high speed in a pulsed manner, and excise or incise living tissue by an impact pressure thereof (see JP-A-2008-82202).
In JP-A-63-99853, since a high-pressure liquid is introduced to the nozzle via the tube having flexibility, even if the pulsed flow is generated by the pump, the liquid is ejected as the continuous flow. When performing incision of living tissue by the continuous flow ejection, the incision is performed so as to open up an operative site by the fluid pressure. Therefore, it is necessary to increase a liquid supply pressure in order to achieve a sufficient incision performance.
According to JP-A-2008-82202, the fluid is transformed into the pulsed flow by the volume varying unit to eject the pulsed flow from the nozzle. In this case, since the incision and excision are performed so as to scrape off living tissue by the impact pressure of a bow wave or fluid particles of the pulsed fluid, a fluid supply pressure may be low, and the quantity of liquid supply may be small as well.
As described above, since the excision performance or excision characteristics with respect to living tissue are different between the continuous flow ejection and the pulsed flow ejection, it is preferable to selectively use the continuous flow and the pulsed flow according to the operative site or the excision characteristics.
Accordingly, selectively using two types of fluid ejection devices for the continuous flow ejection and the pulsed flow ejection is conceivable. However, it is troublesome to selectively use the fluid ejection devices as occasion demands and operability is remarkably lowered.
In the case of the fluid ejection device according to JP-A-2008-82202, when drive of the volume varying unit is stopped, the continuous flow ejection is enabled. However, in this state, a sufficient fluid supply pressure is not obtained and hence the excision performance is lowered. In particular, with a configuration to realize a high-pressure pulsed flow by an inertance effect of the fluid without the provision of a check valve as in the case of JP-A-2008-82202, a conduit is set to have a very small cross-sectional area or to be very long in order to increase the inertance at a part of the flow channel. Therefore, the flow channel resistance is increased, and the ejection at a required pressure can hardly be obtained by the continuous flow ejection even though the drive of the volume varying unit is simply switched.